Rutile dielectric properties

Indeed, the experiements appear to be precise and carefully executed. The same may be said of the careful thermodynamic study of Picard and Gerdanian on slightly reduced rutile, where the results obtained are also treated in terms of point defects. Interpretation in terms of CS planes would seem to be at least as realistic an alternative as point defects, and it is a pity that the authors have not attempted such an analysis. Other recent papers on the physical and chemical properties of reduced rutile, such as that of Baumard on the chemical diffusivity of oxygen in oxygen-deficient rutile, or that of Izumi on dielectric properties, are also analysed in terms of point defects only. Similar criticisms therefore apply to these articles. In contrast, studies of oxygen-tracer diffusion in rutile and the Ti 02 -i phases by Bagshaw and Hyde are presented clearly, with no extrapolations made about the defect structure of the materials used. 

The main electroceramic apphcations of titanium dioxide derive from its high dielectric constant (see Table 6). Rutile itself can be used as a dielectric iu multilayer capacitors, but it is much more common to use Ti02 for the manufacture of alkaline-earth titanates, eg, by the cocalciuation of barium carbonate and anatase. The electrical properties of these dielectrics are extremely sensitive to the presence of small (<20 ppm) quantities of impurities, and high performance titanates require consistently pure (eg, >99.9%) Ti02- Typical products are made by the hydrolysis of high purity titanium tetrachloride. 

The system BaO — T1O2 comprises 5 compounds, three of which have an incongruent melting point. The lowest eutectic melts at 1317 °C. Only two of the compounds mentioned find practical applications BaTi03 and BaTi409. The former is especially significant and will be discussed in detail below. The other compound is one of the correcting phases used in rutile ceramics (see above). In addition, it constitutes abase for linear dielectrics with a low temperature dependence of permittivity. The properties of some of the materials dealt with above are listed in Table 27. 

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